Field of the Invention
The present invention relates to an exhaust gas purification apparatus and method for controlling the same. More particularly, the present invention relates to an exhaust gas purification apparatus and method for controlling the same which adjusts an oxygen purge period after fuel-cut according to a degradation level of a three way catalyst to improve performance of a three way catalyst.
Description of Related Art
Recently, according to an increased usage of vehicles and increased traffic volume, air pollution due to exhaust gas has come to the fore as a serious social problem.
Therefore, governments of every country have set an emission standard of pollutants in exhaust gas such as carbon monoxide (CO), hydrocarbon (HC), nitrogen oxide (NOx) and the like to regulate exhaust gas. Regulations on exhaust gas are becoming more and more strict.
Further, manufacturers of vehicles make a great effort to effectively cope with the regulations on exhaust gas which are becoming stricter. A novel vehicle is manufactured in accordance with an exhaust gas emission standard.
Particularly, to satisfy an exhaust gas emission standard, a three way catalyst converter in which a noble metal is immersed is disposed in an exhaust system of the vehicle to accelerate the oxidation of hydrocarbon, oxidation of carbon monoxide, and reduction of nitrogen oxide.
The three way catalyst refers to a catalyst which simultaneously reacts with a hydrocarbon based compound, carbon monoxide, and nitrogen oxide (NOx) to remove these compounds and a Pt/Rh, Pd/Rh or Pt/Pd/Rh catalyst is mainly used.
The three way catalyst performs a function of reducing carbon monoxide and hydrocarbon or reducing nitrogen oxide in response to a change of a lean (excessive oxygen) state and a rich (excessive fuel) state with respect to the air-fuel ratio of exhaust gas.
In the meantime, in a fuel cut state, unburned air passes through the three way catalyst so that oxygen is stored in the three way catalyst. When fuel is reinjected, the purification rate of nitrogen oxide is significantly lowered due to the stored oxygen. To prevent the lowering of the purification rate, an oxygen purge (O2 purge) function which excessively injects fuel at the time of reinjecting the fuel to consume oxygen is performed.
However, catalyst performance deteriorates as the three way catalyst degrades. When the three way catalyst is controlled in a region that the amount of oxygen storage capacity (OSC) is below a certain value, control becomes difficult since the variation of catalyst performance according to a variation of the OSC is large, therefore deterioration of the catalyst performance such as emissions etc. is generated.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.